1. Technical Field
The present invention relates to a bearing shell having a structured sliding surface, to a tool for machining sliding surfaces of bearing shells, which comprises two cutting cartridges that are mounted on the spindle head of a drilling spindle, and to a method for machining a bearing shell using such a drilling spindle.
2.Related Art
The machining of sliding surfaces of bearing shells is nowadays implemented by means of a so-called drilling out of the bearing shells. A drilling spindle hereby rotates at a rotational speed X [rev/min] and moves at a feed rate Y [mm/rev] in the axial direction. Drilling out is implemented by means of a drilling spindle, inserted in the spindle head of which are two cutting cartridges lying opposite one another at 180°.
A drilling spindle of this kind is shown in FIG. 1. The drilling spindle 20 comprises a first cutting cartridge 21 for cutting the bearing shell 30 to a certain wall thickness and a second cutting cartridge 22 for forming so-called exposed regions (crush relief surfaces) that will be explained below. The cutting cartridges 21 and 22 are arranged axially offset on the spindle head. The diameter of the cutting circle can be adjusted when the drilling spindle 20 is idle. During the machining process, the two cutting cartridges are fixed with respect to their axial direction, i.e. in the radial direction of the drilling spindle 20.
FIG. 2A shows a cross-section (along the dashed and dotted line shown in FIG. 3) of a bearing shell 30. As is shown in FIG. 2A, the sliding surface 31 is flat along the axial direction of the bearing shell. Depending on the machining feed rate in conjunction with the rotational speed of the drilling spindle, a more or less fine but very uniform course of grooves is formed on the sliding surface (not shown in the figures) when machining the sliding surface. The individual grooves extend uniformly and, with the exception of the radius of curvature of the bearing shell, in a flat manner. This phenomenon occurs as a result of the process and is unavoidable when using a cutting tool of the type described above.
An exposed region is to be understood as a region at the ends of the bearing shell, in which the wall thickness of the bearing shell is continuously reduced as compared to the wall thickness of the rest of the bearing shell. In this manner, the wear of a shaft running in the bearing shell, which is due to imprecisions at the connection sites of the two bearing shells that form a bearing, can be reduced.
A further cause of wear on the bearing and the shaft mounted therein is a minimal bending or tilting when a load is applied to the shaft. If the bearing is a connecting rod eye or another bearing that is subject to high loads in internal combustion engines, these uneven loads of the shaft on the bearing ultimately have a disadvantageous effect on the running behaviour of the engine.